Cellular telecommunications network

ABSTRACT

This disclosure provides a base station, and a method of operating a base station, in a cellular telecommunications network, the base station having normal, compensation and energy saving modes of operation.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a National Phase entry of PCT Application No.PCT/EP2017/071645, filed Aug. 29, 2017, which claims priority from EPPatent Application No. 16191524.4 filed Sep. 29, 2016 each of which ishereby fully incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of operating a base stationin a cellular telecommunications network.

BACKGROUND

Cellular telecommunications networks include a network of base stationswhich communicate with User Equipment (UE) within a particular coveragearea. Traditional base stations are often known as macrocells (owing totheir relatively large coverage area over several kilometers squared),but modern cellular networks also include small cells (includingfemtocells, picocells, microcells and metrocells) which have smallercoverage areas than the macrocell. The use of these differenttechnologies allows Network Operators to increase capacity by deployingthe small cell base stations to a large number of customer premises(e.g. homes and businesses), thereby increasing capacity where there isdemand.

Despite the advantages of a mass deployment of small cell base stationswithin a heterogeneous network, Network Operators are conscious of theincreased energy demand of such a large number of base stations.Accordingly, the 3^(rd) Generation Partnership Project (3GPP) introducedan energy saving feature in Technical Specification (TS) 36.300, section22.4.4. In this standard, base stations were designated as either“coverage” or “capacity”. The coverage base station provides basicservice about a large coverage area but also controlled one or morecapacity base stations. The coverage base station may therefore switchthe capacity base stations between normal and energy saving modes ofoperation according to an energy saving policy (such that the capacitybase stations enter energy saving mode when demand is low). The capacitybase stations were also allowed to autonomously switch between thenormal and energy saving mode, but under a policy set by the coveragebase station. The switch off instruction or the policy may also comefrom the Network Operator via the coverage base station. Nonetheless,each base station had one of two defined roles in which it couldoperate.

The energy saving function is further defined in 3GPP TS 32.551. Thisspecification discusses the problem of coverage holes being created whencapacity base stations enter energy saving mode. Accordingly, basestations are also able to enter “compensation” mode, in which the basestation serves one or more UEs previously served by the base stationthat has entered energy saving mode. This may be achieved by a simplehandover of the UEs to the coverage base station, or may be a handoverto a new base station (e.g. a neighboring base station). Thecompensation base station may also require a substantial change in itscoverage area in order to serve the new UEs.

A further 3GPP specification, TR 36.927, discusses potential solutionsfor energy saving and highlights policies for “re-activation” of basestations (i.e. exiting energy saving mode). These policies include:

No assistance—in which the coverage base station instructs the capacitybase station to exit energy saving mode without any knowledge of itslocal conditions;

Reactivation based on load;

Reactivation based on Interference over Thermal (IoT) measurements;

Reactivation based on UE measurements; and

Reactivation based on UE and base station locations.

SUMMARY

According to a first aspect of the disclosure, there is provided amethod of operating a base station in a cellular telecommunicationsnetwork, the base station having normal, compensation and energy savingmodes of operation and being configured to switch between the normal,compensation and energy saving modes of operation, the method comprisingthe first base station sending a first message to a second base station,the first message including energy saving mode data for the first basestation indicating that the first base station is of a first networkoperator's network; the first base station receiving a second message,the second message being responsive to the energy saving mode data; andthe first base station determining whether to enter the energy savingmode of operation based on the second message. The energy saving modedata may relate to the first base station requesting that the secondbase station act in compensation mode for the first base station.

According to a second aspect of the disclosure, there is provided amethod of operating a base station in a cellular telecommunicationsnetwork, the base station having normal, compensation and energy savingmodes of operation and being configured to switch between the normal,compensation and energy saving modes of operation, the method comprisingthe first base station receiving a first message from a second basestation, the first message including energy saving mode data for thesecond base station indicating that the second base station is of afirst network operator's network; and the first base station making adetermination of whether to enter the compensation mode of operationbased on the first message. The energy saving mode data may relate tothe second base station requesting that the first base station act incompensation mode for the second base station.

Accordingly, a base station of another Network Operator may compensatefor the base station entering energy saving mode if a suitable NeutralHosting Arrangement, NHA, is, or can be, established. The decision onwhich base station to reactivate (and the parameters of thereactivation) may also be based on the NHA.

According to a third aspect of the disclosure, there is provided amethod of operating a base station in a cellular telecommunicationsnetwork, the base station having normal, compensation and energy savingmodes of operation and being configured to switch between the normal,compensation and energy saving modes of operation, the method comprisingthe first base station sending a first message to a second base station,the first message including energy saving mode data for the first basestation, the energy saving mode data relating to the first base stationrequesting that the second base station act in compensation mode for thefirst base station; the first base station receiving a second message,the second message being responsive to the energy saving mode data forthe first base station, and including energy saving mode data for thesecond base station including a request that the first base station actin compensation mode for the second base station; and the first basestation entering compensation mode and compensating for the second basestation.

According to a fourth aspect of the disclosure, there is provided amethod of operating a base station in a cellular telecommunicationsnetwork, the base station having normal, compensation and energy savingmodes of operation and being configured to switch between the normal,compensation and energy saving modes of operation, the method comprisingthe first base station receiving a first message from a second basestation, the first message including energy saving mode data for thesecond base station including a request that the first base station actin compensation mode for the second base station; the first base stationsending a second message to the second base station, the second messageincluding energy saving mode data for the first base station including arequest that the second base station act in compensation mode for thefirst base station; and the first base station entering energy savingmode.

Embodiments of the third and fourth aspects of the present disclosuretherefore provide the advantage that base stations may negotiate withother base stations to determine which base station should become thecompensator.

According to a fifth aspect of the disclosure, there is provided acomputer program comprising instructions which, when the program isexecuted by a computer, cause the computer to carry out the method inany one of the first, second, third or fourth aspects of the disclosure.

According to a sixth aspect of the disclosure, there is provided a basestation comprising a transceiver, a processor and memory, wherein theprocessor is configured to perform the method of any one of the first,second, third or fourth aspects of the disclosure. The base station maybe part of a cellular telecommunications network.

BRIEF DESCRIPTION OF THE FIGURES

In order that the present disclosure may be better understood,embodiments thereof will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a first embodiment of a cellulartelecommunications network.

FIG. 2 is a schematic diagram of a base station of the network of FIG.1.

FIG. 3 is a schematic diagram of a second embodiment of a cellulartelecommunications network.

FIG. 4 is a schematic diagram of the network of FIG. 3 following atransition in base station operational mode.

FIG. 5 is a table representing data in a Neighbour Relations Table (NRT)of a base station of FIG. 4.

FIG. 6 is a schematic diagram of the network of FIG. 4 following afurther transition in base station operational mode.

FIG. 7 is a table representing data in an NRT of a base station of FIG.6.

FIG. 8 is a schematic diagram of a third embodiment of a cellulartelecommunications network.

FIG. 9 is a schematic diagram of the network of FIG. 8 following atransition in base station operational mode.

FIG. 10 is a table representing data in an NRT of a base station of FIG.9.

FIG. 11 is a schematic diagram of a fourth embodiment of a cellulartelecommunications network.

FIG. 12 is a schematic diagram of the network of FIG. 11 following atransition in base station operational mode.

DETAILED DESCRIPTION OF EMBODIMENTS

A cellular telecommunications network 1 of a first embodiment of thedisclosure is illustrated in FIG. 1. The network 1 includes a first basestation 10, which in this embodiment is an evolved Node B (hereinafter,“eNB”) and second, third and fourth base stations 20, 30, 40, which inthis embodiment are Home eNBs, which are otherwise known as small cells,or femtocells, picocells, metrocells, or microcells depending on thecoverage area. For the remainder of this specification, these basestations will be referred to as the first, second, third and fourth eNB10, 20, 30, 40, respectively. The base stations' coverage areas areillustrated by the enveloping ellipses, which represent the propagationdistances for signals transmitted by each base station to one or moreUEs. In FIG. 1, a single UE 50 a, 50 b, 50 c, 50 d is connected to eachbase station, although in practice each base station can be connected tomany UEs. In this embodiment, the base stations use the 4^(th)Generation (4G) Long-Term Evolution (LTE) protocol for suchtransmissions.

The eNBs 10, 20, 30, 40 are also connected to at least one Core Network(not shown) of a Network Operator. If the base station is connected tomultiple Core Networks (e.g. two or more Core Networks of two or morerespective Network Operators using the SI-flex protocol), then the basestation hardware may be used by either Operator.

FIG. 2 is a schematic diagram representing various components of thefirst eNB 10. The first eNB 10 includes a first transceiver 11, aprocessor 13, a memory 15, and a second transceiver 17, all connectedvia bus 19. The first transceiver 11 is commonly known as the backhaulconnection and is used for transmissions to and from the Core Network,which would typically be via a carrier-grade Ethernet or fiberconnection for the first eNB 10. The second transceiver 17 is an antennaconfigured for cellular communications (in this embodiment, via the 4GLTE protocol) with any connected UEs. The processor 13 typicallyprocesses data packets received via the first transceiver 11 or secondtransceiver 17 such that they are in a form to be transmitted to theirdestination (for example, IP data packets received at the firsttransceiver 11 from the Core Network may be processed into TransportBlocks (TBs) by the processor 13 for onward transmission to a UE via thesecond transceiver 17, which may be temporarily stored in a buffer inmemory 15).

In this embodiment, the first eNB 10 has three defined modes ofoperation. The first mode is hereinafter known as “normal” mode.Characteristics of normal mode include:

-   -   the first eNB 10 is configured to transmit physical broadcast        channel signals (e.g. reference signals);    -   the first eNB 10 is configured to accept connections from UEs;    -   the first eNB 10 is configured to serve any connected UEs, such        as by forwarding any messages between the UE and the Core        Network; and    -   the first eNB 10 is configured to transmit signals to any        connected UEs via the transceiver 11 using a range of power        levels defined by its operational protocol.

The skilled person will understand that this mode of operation iscommonly used by base stations and the energy usage of any particularbase station in this mode can vary based on, for example, the number ofconnected UEs, the distances of the connected UEs to the base station,and the data requirements of the connected UEs.

The second mode of operation of the first eNB 10 is hereinafter known as“energy saving mode”. Characteristics of energy saving mode include:

-   -   the first eNB 10 does not transmit physical broadcast channel        signals, or transmits fewer physical broadcast channel signals        (compared to normal mode)    -   the first eNB 10 does not accept connections from UEs, or is        configured to accept a reduced number of connections from UEs        (compared to normal mode);    -   the first eNB 10 does not serve any UEs, or is configured to        serve a reduced number of UEs (compared to normal mode);    -   the first eNB 10 reduces the number of processes performed by        processor 13 (compared to normal mode); and    -   the first eNB 10 does not transmit signals to any connected UEs,        or is configured to transmit to any connected UE at a relatively        low power level (compared to normal mode).

The skilled person will understand, based on the above teaching, thatthe energy saving mode of operation is therefore used to reduce theenergy consumption of a base station. The base station operating inenergy saving mode will therefore use less energy than the same basestation operating in normal mode in substantially similar conditions.

The first eNB 10 should avoid switching from normal to energy savingmode when it has a connected UE, as that UE may suddenly experience areduced Quality of Service (QoS), or no service should the first eNB 10be configured to not serve the UE at all when in energy saving mode.Accordingly, the first eNB 10 must manage its transition to energysaving mode to avoid a reduction in QoS for any connected UE. This mayinclude a passive transition in which no new connections from UEs areaccepted and the first eNB 10 waits for any connected UEs to disconnectand handover to another base station. Alternatively, this may be anactive transition in which no new connections from UEs are accepted andthe first eNB 10 causes the UEs to handover to another base station.

The third mode of operation of the first eNB 10 is known as“compensation mode”. The characteristics of compensation mode aresimilar to normal mode, but further include:

-   -   the first eNB 10 is configured to accept connections from UEs        that were previously served by a base station that is entering        (or has entered) energy saving mode;    -   the first eNB 10 serves any UEs that were previously served by a        base station that is entering (or has entered) energy saving        mode; and    -   the first eNB 10 modifies its configuration in order to take the        responsibilities of the base station entering energy saving        mode, which may include one or more of:        -   the first eNB 10 modifying its coverage area (e.g. increases            its coverage area by increasing the upper limit of its power            range of transmissions from the second transceiver 17) to            serve the UEs that were previously served by a base station            that has entered energy saving mode;        -   the first eNB 10 increasing its processing power;        -   the first eNB 10 increasing its radio capacity (such as by            using previously disabled antennas); and        -   the first eNB 10 adopting different services (e.g. a            different protocol).

This compensation mode is therefore used by the first eNB 10 tocompensate for the loss of coverage and/or service that was theresponsibility of the other base station that is now entering energysaving mode. Although this may result in an increase in energyconsumption for the first eNB 10, any such increases are generally morethan offset by the overall reduction in energy consumption in thenetwork 1 as a result of one or more other base stations entering energysaving mode.

In this embodiment, the first eNB 10 is able to switch between the threemodes of operation (e.g. between normal and compensation mode and viceversa, between normal and energy saving mode and vice versa, and betweenenergy saving mode and compensation mode and vice versa). Any change inoperational mode may be effected by the base station adopting one ormore of the characteristics outlined above.

In this embodiment, the second, third and fourth eNB 20, 30, 40 have asimilar construction as outlined above for the first eNB 10. The skilledperson will understand that some physical elements of the eNBs 20, 30,40 may differ to the first eNB 10 (as they are Home eNBs in thisembodiment), but the concepts above of the normal, energy saving andcompensation modes of operation apply equally to the second, third andfourth eNBs 20, 30, 40.

Embodiments of methods of the present disclosure will now be describedbased on the network elements described above. In these embodiments,base stations are able to negotiate changes in their mode of operation.

A first embodiment of the present disclosure will now be described withreference to FIGS. 3 to 7. In this embodiment, the first, second, thirdand fourth eNBs 10, 20, 30, 40 are all operating in normal mode, are allconnected to a Core Network of a single Network Operator, and are eachcommunicating with at least one UE 50 a, 50 b, 50 c, 50 d. Furthermore,each base station stores a Neighbor Relations Table, NRT, in memory,which stores identifying information regarding each base station (suchas the evolved Cell Global Identifier, eCGI, and other X2 connectioninformation) in the network 1. The NRT is also used to store datarelating to the operational mode of each neighboring base station(details of the structure of this data and the mechanisms for updatingit are described later in this description).

In this embodiment, the third eNB 30 determines that it should enterenergy saving mode. This determination is made by the processor and maybe triggered upon, for example, its load being below a threshold.Following this determination, the third eNB 30 looks up the identifyingeCGIs of its neighbor base stations, sets up an X2 connection (e.g. byquerying the Mobility Management Entity, MME, of the Core Network withthe eCGI) with each neighboring base station if one has not already beenestablished, and sends a first X2 message to each base station. Thefirst X2 message includes:

-   -   an indication that the third eNB 30 intends on entering energy        saving mode;    -   a request for the base station receiving the first X2 message to        compensate for the third eNB 30;    -   an indication of the number of UEs connected to the third eNB 30        (just one in this example);    -   location information of the third eNB 30 (e.g. Global Navigation        Satellite System, GNSS, coordinates);    -   a measure of the third eNB's power level;    -   an indication of the third eNB's load (this may be current and        forecast);    -   an indication of the third eNB's required level of compensation        (e.g. guaranteed full coverage, best effort compensation,        compensation for existing UEs only); and    -   an estimate of a time period that the third eNB intends on being        in energy saving mode for.

Each base station receiving the first X2 message then makes adetermination, based on the data in the first X2 message, whether it cancompensate for the third eNB 30. In this example, the second eNB 20makes a positive determination and responds to the first X2 message witha second X2 message indicating that the second eNB 20 will compensatefor the third eNB 30.

The third eNB 30 then sends a third X2 message to the second eNB 20which includes data regarding the third eNB 30 (hereinafter known as“compensation data”). In this embodiment, this compensation dataincludes:

-   -   the third eNB's capabilities, such as        -   its configuration (i.e. maximum power, E-UTRAN Absolute            Radio-Frequency Channel Numbers (EARFCNs), etc.);        -   its services (i.e. 2/3/4G, WiFi, VoLTE, VoWiFi, voice,            video, etc.)        -   its QoS (i.e. guarantees regarding reliability, latency,            etc.)    -   the eCGI of each base station that has offered to compensate for        the third eNB 30 (just the second eNB 20 in this example);    -   information regarding its neighboring base stations (e.g. eCGI,        PCI, X2 information);    -   an identifier (e.g. IMSI) of each UE that the third eNB 30        serves; and    -   a power consumption reading for the third eNB (this could be        split into several readings identifying, for example, average        and peak power consumptions, power consumption in energy saving        mode, power consumption when particular services are active,        etc.).

On receipt of the third X2 message, the second eNB 20 knows that it isthe only base station that will compensate for the third eNB 30 (as itis the only base station identified in the third X2 message as willingto compensate) and must therefore provide full compensation for itsservices and coverage. This may be contrasted to the case, describedlater in this description, in which there are multiple compensators.Furthermore, as shown in FIG. 3, the second eNB 20 does not need tomodify its coverage area in order to provide coverage and service forthe UE 50 c.

Once the third X2 message has been successfully sent to the second eNB20 (which may be indicated using acknowledgment messages), then thethird eNB 30 starts its transition to energy saving mode. Thistransition includes the following:

-   -   the third eNB 30 instructs its connected UE 50 c to handover to        the second eNB 20;    -   the third eNB 30 sends a fourth X2 message to all neighboring        base stations in its NRT indicating that it is entering energy        saving mode and that the second eNB 20 is the compensating base        station; and, following a successful handover of the UE 50 c,    -   entering energy saving mode (such as by adopting one or more of        the characteristics outlined above).

Upon receipt of the fourth X2 message at the second eNB 20, the secondeNB 20 is configured to send a fifth X2 message to all neighboring basestations of the third eNB 30 (as identified previously in the X2message, which may require first establishing the necessary X2connection) and to the Operations and Management (OAM) module of theCore Network. The fifth X2 message contains all data values from thethird X2 message.

The NRT data will now be described in more detail. As noted above, eachneighboring base station of the third eNB 30 receives the first andfourth X2 messages, and each neighboring base station receives the datacontained in the third X2 message either from the third X2 message (forthe second eNB 20) or from the fifth X2 message (for all otherneighboring base stations). Each base station contains an NRT in memory,and this is updated with information upon receipt of these messages. TheNRT of this embodiment therefore contains more information than a basicNRT of the prior art. The base stations therefore store commoninformation in their NRTs regarding their neighboring base stations andother data relevant for the present disclosure. The relevance of thisdata will become apparent when discussing re-activation later in thedescription.

FIG. 4 illustrates the state of the network 1 following the switch ofthe third eNB 30 to energy saving mode and of the second eNB 20 tocompensation mode. As shown, the third eNB 30 no longer has anenveloping ellipse as it is no longer transmitting signals about acoverage area. The UE 50 c is now served by the second eNB 20. Anexample of the common data stored in the NRT of each base station isshown in FIG. 5.

At a subsequent time, the second eNB 20 also determines that it shouldswitch from compensation mode to energy saving mode. This, again, may bedetermined following the second eNB's 20 load dropping below athreshold. Similar to the technique used above, the second eNB 20 looksup the identifying eCGIs of its neighbor base stations, sets up an X2connection (e.g. by querying the Mobility Management Entity, MME, of theCore Network with the eCGI) with each neighbor if one hasn't alreadybeen established, and sends a first X2 message to each base station. Asin the example above, the first X2 message includes an indicator thatthe second eNB 20 intends on entering energy saving mode, a request forthe base station receiving the first X2 message to compensate for thesecond eNB 20, and data relevant for the neighboring base stations tomake a determination of whether they can compensate for the second eNB20.

As the second eNB 20 is already compensating for the third eNB 30, thefirst X2 message includes the data points identified above (that is, anidentifier, a request for compensation, an indication of the number ofUEs and load, and location information) for both the second eNB 20 andthe third eNB 30.

In this embodiment, the second eNB 20 receives second X2 messages fromboth the first eNB 10 and the fourth eNB 40. These messages indicatethat the first eNB 10 and fourth eNB 40 will compensate for the secondeNB 20. In response, the second eNB 20 sends third X2 messages to boththe first eNB 10 and fourth eNB 40 including compensation data. Thiscompensation data includes the information discussed above, andtherefore informs the neighboring base stations that both the first eNB10 and fourth eNB 40 are to compensate for the second and third eNBs 20,30.

When the first eNB 10 and fourth eNB 40 receive this third X2 message,the first eNB 10 is informed that the fourth eNB 40 will also compensateand vice versa. Accordingly, the first eNB 10 and fourth eNB 40 exchangemessages to determine how the services and coverage of the second andthird eNBs 20, 30 should be shared. In this example, the two basestations decide that the capabilities of the third eNB 30 should becompensated for by the fourth eNB 40 and the capabilities of the secondeNB 20 should be compensated for by the first eNB 10 (this is based onthe location data of the base stations as discovered in the compensationdata).

In this embodiment, the coverage area of the fourth eNB 40 does notcover UE 50 c of the third eNB 30. However, the fourth eNB 40 is able toestimate an increase in transmission power required to compensate forthe third eNB 30 going into energy saving mode. In this embodiment, theincrease in transmission power is based on the power level of the thirdeNB 30 plus an estimated propagation loss between the third and fourtheNBs 30, 40. The propagation loss may be estimated based on the distancebetween the two base stations (which has been identified by the GNSScoordinates from the first X2 message), or alternatively the fourth eNB40 may measure the signal strength of the third eNB 30 and thepropagation loss will be the difference between the transmission power(identified in the first X2 message) and the measured signal strength.The fourth eNB 40 may then increase its transmission power by acorresponding amount.

Once the third X2 message has been successfully sent to the first eNB 10and fourth eNB 40 (which again may be confirmed with acknowledgementmessages), then the second eNB 20 starts its transition to energy savingmode. This transition includes:

-   -   the second eNB 20 instructs its connected UEs 50 b, 50 c to        handover to the first eNB 10 and fourth eNB 40 respectively;    -   the second HeNb 20 sends a fourth X2 message to all neighboring        base stations in its NRT indicating that it is entering energy        saving mode and that the first eNB 10 and fourth eNB 40 are        compensating base stations; and, following a successful handover        of the UEs 50 b, 50 c,    -   entering energy saving mode (such as by adopting one or more the        characteristics outlined above).

Upon receipt of the fourth X2 message at the first eNB 10 and fourth eNB40, both base stations send a fifth X2 message to all neighboring basestations of the second eNB 20 (as identified previously in the NRT ofthe third X2 message) and to the OAM of the Core Network. The fifth X2message contains all data values from the third X2 message, such thatthe neighboring base stations can update their NRTs with the latestcompensation data (including the configuration change of the fourth eNB40).

FIG. 6 illustrates the state of the network 1 following this transition.As shown, the second and third eNBs 20, 30 no longer have envelopingellipses as they are no longer transmitting signals about a coveragearea. The UEs 50 b, 50 c are now served by the first eNB 10 and fourtheNB 40, respectively (with the fourth eNB's 40 coverage area suitablyincreased). FIG. 7 illustrates the data contained in the NRT of eachbase station following this transition. The data identifies the thirdeNB 30 as an “inherited” base station. The third eNB 30 is inherited inthe sense that the first eNB 10 is now compensating for that basestation, but another base station was previously compensating for it.The data also identifies the power increase required for the fourth eNB40 to act in compensation mode for it.

There are further examples of how two base stations may negotiate theirstatus between the three operational modes than those described above.For example, on receipt of the first X2 message, all neighboring basestations may indicate (via the second X2 message) that they cannotcompensate for the base station making the request. The requesting basestation will therefore not go into energy saving mode. This isadvantageous over the prior art as it is therefore not possible for abase station to go into energy saving mode and put an impossible strainon its neighbors.

Furthermore, on receipt of the first X2 message, the neighboring basestation may also send a first X2 message back to the original basestation. The two base stations may then negotiate which of the twoshould go into energy saving mode and which should go into compensationmode. It may therefore transpire that the base station sending theoriginal first X2 message compensates for the neighboring base station,and may also inherit further base stations to compensate for.

In another scenario, the neighboring base station may indicate that adifferent base station may compensate for it. Furthermore, followingreceipt of the first X2 message, the neighboring base station maynegotiate with other neighboring base stations which one (or several)should compensate for the requesting base station.

As can be seen from the above examples, there is no longer the definedlinkage between “coverage” base stations and “capacity” base stations,in which the coverage base station controls the energy saving state ofthe capacity base station, as in the prior art. Instead, the presentinvention proposes a mechanism by which base stations can switch betweenany one of the three modes of operation (normal, energy saving,compensation), and compensation can be provided dynamically by one onmore if its neighboring base stations.

In the above examples, the first X2 message is sent to all theneighboring base stations in the NRT. However, this is non-essential. Inother embodiments, the first X2 message may be sent to a single neighboror a subset of neighbors. The choice of neighbors may be based on knowncharacteristics of the neighbor (e.g. their location) or their priorperformance when acting as a compensator (e.g. based on measurable KeyPerformance Indicators, KPIs, during said prior performance).

In the above embodiments, the neighboring base station makes adetermination on whether to become a compensator for another basestation following receipt of the first X2 message. This determinationmay be based on, for example:

-   -   the base station's current and forecast load;    -   the current and forecast load in the area of the base station;    -   the base station's power consumption;    -   the base station's estimated energy increase to compensate for        the other base station; and    -   KPIs of prior performances when acting as compensator for the        other base station.

Furthermore, a base station may store a measure of its KPIs when actingas a compensator for another base station in memory. This may also beassociated with its configuration profile at that time. Accordingly,upon future requests to compensate for the other base station, the basestation may reconfigure to use that configuration profile.

A further embodiment of the present disclosure will now be described,with reference to FIGS. 8 to 10. The starting point for the followingexample is based on the network as described in the previous embodimentand shown in FIG. 8 (such that the second and third eNBs 20, 30 are inenergy saving mode and the first eNB 10 and fourth eNB 40 arecompensating for those base stations).

At a subsequent point in time, a decision is made to re-activate thethird eNB 30 as the load on the first eNB 10 is above a threshold. Inthis embodiment, the decision is made by the first eNB 10 and not onlycauses the third eNB 30 to switch out of energy saving mode, but alsocauses the third eNB 30 to compensate for the second eNB 20.Accordingly, the first eNB 10 sends a sixth X2 message to the third eNB30, which includes:

-   -   an instruction for the third eNB 30 to switch out of energy        saving mode;    -   compensation data for the second eNB 20;    -   an instruction for the third eNB 30 to enter compensation mode        and compensate for the second eNB 20.

The third eNB 30 reacts to these instructions by switching from energysaving mode to compensation mode (by adopting one or more of thecharacteristics outlined above), which in this example involves amodification of its transmission power in order to cover the second eNB20. This modification may be calculated in a similar manner as describedin the previous embodiment.

The first eNB 10 updates its NRT to reflect the above changes.Furthermore, the first eNB 10 sends a seventh X2 message to allneighboring base stations of the third eNB 30 to inform them that thethird eNB 30 has reactivated and that the third eNB 30 is nowcompensating for the second eNB 20. All neighboring base stations updatetheir records in their NRT.

Also, the fourth eNB 40 reacts to the seventh X2 message by switchingfrom compensation mode to normal mode (as it no longer needs tocompensate for the third eNB 30). In this embodiment, this switchinvolves a reversal of the configuration changes applied by the fourtheNB 40 when compensating for the third eNB 30.

Following these changes, the network is as shown in FIG. 9. The fourtheNB 40 has reduced its coverage area to its previous state and is nolonger compensating for the third eNB 30, the first eNB 10 is no longercompensating for the second or third eNB 20, 30, and the third eNB 30has modified its coverage area to compensate for the second eNB 20.

The information stored in each NRT of the base stations is shown in FIG.10.

In this embodiment, a determination was made by the first eNB 10 toreactivate the third eNB 30 and for the third eNB 30 to thereaftercompensate for the second eNB 20. As discussed above, each base stationrecords in its NRT various data points regarding each base station inthe network, including the configuration parameters of the base stationsin energy saving mode, and any configuration changes the compensatingbase station needed to make in order to compensate. The determination onwhether a base station should reactivate another base station can bemade based on this data. In this manner, an informed decision can bemade on which base station to reactivate in order to appropriatelybalance the capacity and energy consumption of the network, or such thatthe services offered by the reactivated base station is such that it maycompensate using an appropriate configuration (e.g. based on theservices required), the reactivated base station can be reactivatedusing the appropriate configuration parameters, and the compensationbase station can be reconfigured to its previous state.

In alternative arrangements, the decision to reactivate a base stationin an energy saving state can be made by another entity than thecompensating base station—such as another base station, an entity in theCore Network, or the energy saving base station itself. In thesealternative arrangements, it is preferable that information that such anevent has occurred be recorded in each base station's NRT. This can beachieved by the entity instructing the base station to exit energysaving mode sending messages to its neighbors (equivalent to the seventhX2 message in the embodiment above), or each base station polling anenergy saving base station to determine if it has reactivated.

Another embodiment of the disclosure will now be described withreference to FIGS. 11 to 12. This embodiment includes a cellular network101, having first, second, third and fourth eNBs 110, 120, 130, 140 andtheir respective UEs 150 a, 150 b, 150 c, 150 d. These components aresubstantially similar in construction as those described in the previousembodiments.

Also shown in FIG. 11 is a first and second Core Network, controlled byNetwork Operator A and Network Operator B, respectively. The third andfourth eNBs 130, 140 are connected to Network Operator A′s Core Network,the first eNB 110 is connected to Network Operator B's Core Network, andthe second eNB 120 is connected to both Network Operator A and B's CoreNetworks (e.g. via S1 flex). The second eNB 120 is primarily serving thesecond Network Operator, but has a Neutral Hosting Agreement (NHA) whichallows it to serve UEs of the first Network Operator.

The network 100 is initially in a state as shown in FIG. 11, such thatall base stations are in their normal mode of operation and are servingtheir respective UEs. Each base station includes an NRT in its memory,which stores identifying information (e.g. eCGI) of all neighboring basestations. This typically stores data of base stations operated by thesame Network Operator, but may also include data of base stationsoperated by other Network Operators if an NHA and suitable S1-flexconnection have been established. Accordingly, the first eNB 110 storesdata on the other base station of the second Network Operator (thesecond eNB 120), the second eNB 120 stores data on the other basestations of the first and second Network Operators (the first, third andfourth eNBs 110, 130, 140), the third eNB 130 stores data on the otherbase stations of the first Network Operator (the second and fourth eNB120, 140), and the fourth eNB 140 stores data on the other base stationsof the first Network Operator (the second and third eNB 120, 130).

At a subsequent point in time, the third eNB 130 determines that itshould enter energy saving mode. The third eNB 130 therefore compilesand issues a first X2 message, including:

-   -   an indication that the third eNB 130 intends on entering energy        saving mode;    -   a request for another base station to compensate for the third        eNB 130;    -   an indication of the number of UEs connected to the third eNB        130 (just one in this example);    -   location information of the third eNB 130 (e.g. Global        Navigation Satellite System, GNSS, coordinates);    -   a measure of the third eNB's power level;    -   an indication of the third eNB's load (this may be current and        forecast);    -   an estimate of a time period the third eNB 130 is intending on        being in energy saving mode for;    -   an indication of the third eNB's required level of compensation        (e.g. guaranteed full coverage, best effort compensation,        compensation for existing UEs only);    -   an indication of the third eNB's 130 primary operator (NO-A in        this example); and    -   an indication of other operators the third eNB 130 may operate        for (NO-B in this example).

The first X2 message is sent to each base station in the third eNB's 130NRT—the second and fourth eNB 120, 140. Both base stations respond witha second X2 message indicating that they will compensate for the thirdeNB 130.

As described above for a previous embodiment, the third eNB 130 sends athird X2 message to each base station that has responded positively.This includes the eCGI of each base station that has offered tocompensate for the third eNB 130, and an identifier of the NetworkOperator that owns it. This triggers a negotiation between the secondand fourth eNBs 120, 140 to determine which base station shouldcompensate for the third eNB 130. As noted above, the second eNB 120 isprimarily serving the second Network Operator, but has a NHA such thatit may also serve the first Network Operator. The fourth eNB 140 servesthe same Network Operator, but must increase its coverage area by agreater amount (and therefore energy consumption) than the second eNB120 in order to compensate for the third eNB 130. Accordingly, the twobase stations determine that the second eNB 120 should compensate forthe third eNB 130 (this determination may also be based on the financialimplication of the second eNB 120 being the compensator, based on theNHA).

Following this determination, the method proceeds as in the previousembodiments such that all base stations are updated with thecompensation data, the second eNB 120 increases its coverage area tocompensate for the third eNB 130, the third eNB's UE is handed over tothe second eNB 120, and the third eNB 130 enters energy saving mode. Inthis embodiment, the compensation data includes an indication that thereis a NHA in place between the Network Operators, and includes details ofthe NHA (e.g. maximum data rates, time of expiry etc.). The state of thenetwork following this transition is shown in FIG. 12.

At a subsequent time, a determination may be made to reactivate thethird eNB 130. The determination is again made on the compensation data,which in this embodiment includes details of the NHA between the energysaving base station's Network Operator and the compensating basestation's Network Operator. For example, if the NHA is to end in thenext hour, then the compensating base station may instruct the energysaving base station to exit energy saving mode.

In the above embodiment, the NHA between the first and second NetworkOperators is already in place. However, in an alternative arrangement,the NHA could be established and/or negotiated between the two NetworkOperators upon receipt of the first X2 message. For example, an S1 flexconnection could be established between the two Network Operators, andthe relevant parameters of a new NHA could be negotiated, in order forthe base station to compensate for a base station of another network.

In the above embodiments, the base stations negotiate and control theirmodes of operation via several new inter-base station messages carriedover the X2 protocol. However, this is not essential. For example, thedata contained in the messages defined above may be based onmodifications of existing inter-base station messages used in currentcellular networks. Furthermore, these messages may be contained in thesame or distinct signals.

Furthermore, it is also non-essential that the method of the aboveembodiments of the disclosure be carried out in a distributed manner.For example, all of the above messages could be routed through acentralized entity (such as an Operations and Management (OAM) node ofthe Core Network), which stores and processes the data in order todetermine which base stations should be in the particular modes ofoperation. In this manner, the OAM node may determine which allocationof modes of operation amongst the network of base stations results insuitable coverage and capacity for the network whilst keeping energyconsumption to a minimum.

In the above embodiments, the base stations are all eNBs. However, anyform of base station is suitable for embodiments of the presentdisclosure (e.g. a base station of any cellular telecommunicationsprotocol, including small cells). Furthermore, the functionality of thebase station may be split between different entities, such that acentralized entity performs some functions (typically processing thehigher levels of the protocol stack), whilst one or more remote radiosperform other functions (typically processing the lower levels of theprotocol stack).

In the above embodiments, the base stations either wait for theirconnected UEs to disconnect, or cause their connected UEs to disconnect,prior to entering energy saving mode. The base station may cause the UEsto disconnect either by an explicit message or by gradually reducingtheir transmission power in order to trigger a handover by the UE.

In the above embodiments, a compensation base station instructs anenergy saving base station to exit energy saving mode. Thereafter, thecompensation base station enters normal mode as it no longer has tocompensate for that base station. However, the skilled person willunderstand that the compensation base station may be compensating formultiple energy saving base stations, and may instruct one or a subsetof these to exit energy saving mode. Accordingly, the compensation basestation may still be in compensation mode following a reactivationevent.

The skilled person will understand that any combination of elements ispossible within the scope of the invention, as claimed.

The disclosure may be defined by the following clauses:

1. A method of operating a base station in a cellular telecommunicationsnetwork, the base station having normal, compensation and energy savingmodes of operation, the method comprising: a first base station beingconfigured to switch between the normal, compensation and energy savingmodes of operation.

2. A method as defined in clause 1, further comprising: the first basestation sending a first message to a second base station, the firstmessage including energy saving mode data for the first base station;the first base station receiving a second message, the second messagebeing responsive to the energy saving mode data; and the first basestation determining whether to enter the energy saving mode of operationbased on the second message.

3. A method as defined in clause 2, wherein the energy saving mode datarelates to the first base station requesting that the second basestation act in compensation mode for the first base station.

4. A method as defined in clause 3, wherein the second message indicatesthat the second base station will act in compensation mode for the firstbase station.

5. A method as defined in clause 3 or clause 4, wherein the secondmessage indicates that a third base station will act in compensationmode for the first base station.

6. A method as defined in clause 4 or clause 5, further comprising: thefirst base station entering energy saving mode.

7. A method as defined in clause 3, wherein the second message indicatesthat the second base station will not act in compensation mode for thefirst base station.

8. A method as defined in clause 3, wherein the second message includesenergy saving mode data for the second base station including a requestthat the first base station act in compensation mode for the second basestation.

9. A method as defined in clause 8, further comprising: the first basestation entering compensation mode and compensating for the second basestation.

10. A method as defined in clause 6 when dependent on clause 4, furthercomprising: the first base station sending a third message to the secondbase station, the third message including compensation data for thefirst base station.

11. A method as defined in clause 6 when dependent on clause 5, furthercomprising: the first base station sending a third message to the thirdbase station, the third message including compensation data for thefirst base station.

12. A method as defined in either clause 10 or clause 11, wherein thecompensation data relates to the first base station's configurationparameters.

13. A method as defined in any one of clauses 10 to 12, wherein thecompensation data relates to a fourth base station that the first basestation is acting in compensation mode for.

14. A method as defined in clause 6 or any one of clauses 10 to 13,further comprising: the first base station receiving a fourth message,the fourth message instructing the first base station to exit energysaving mode; and the first base station switching from energy savingmode to normal mode.

15. A method as defined in clause 14 when dependent on clause 13,wherein the fourth message instructs the first base station to act incompensation mode for the fourth base station, the method furthercomprising: the first base station entering compensation mode for thefourth base station.

16. A method as defined in clause 14 or clause 15, wherein the fourthmessage instructs the first base station to act in compensation mode fora fifth base station, the method further comprising: the first basestation entering compensation mode for the fifth base station.

17. A method as defined in clause 1, further comprising: the first basestation receiving a first message from a second base station, the firstmessage including energy saving mode data for the second base stationincluding a request for the first base station to act in compensationmode for the second base station; and the first base station making adetermination of whether to enter the compensation mode of operationbased on the first message.

18. A method as defined in clause 17, wherein the first base stationdetermines that it will compensate for the second base station, themethod further comprising: the first base station sending a secondmessage to the second base station, the second message indicating thatthe first base station will compensate for the second base station.

19. A method as defined in clause 18, wherein the first base stationdetermines that it will not compensate for the second base station, themethod further comprising: the first base station sending a secondmessage to the second base station, the second message indicating thatthe first base station will not compensate for the second base station.

20. A method as defined in either clause 18 or clause 19, furthercomprising: the first base station determining that a third base stationwill act in compensation mode for the second base station; and the firstbase station sending a second message to the second base station, thesecond message indicating that the third base station will compensatefor the second base station.

21. A method as defined in clause 19, further comprising: the first basestation sending a second message to the second base station, the secondmessage including energy saving mode data for the first base stationincluding a request that the second base station act in compensationmode for the first base station.

22. A method as defined in clause 21, further comprising: the first basestation entering energy saving mode.

23. A method as claimed in either clause 18 or clause 20, when dependenton claim 18, further comprising: the first base station receiving athird message, the third message including compensation data for thesecond base station.

24. A method as defined in clause 23, wherein the compensation datarelates to the second base station's configuration parameters.

25. A method as defined in clause 24, wherein the compensation datarelates to a fourth base station that the second base station iscompensating for.

26. A method as defined in clause 25, further comprising: the first basestation acting in compensation mode for the fourth base station.

27. A method as defined in either clause 18, clause 20 when dependent onclause 18, or any one of clauses 23 to 26, further comprising: the firstbase station sending a fourth message to the second base station, thefourth message instructing the second base station to exit energy savingmode.

28. A method as defined in clause 27 when dependent on clause 26,wherein the fourth message instructs the second base station to act incompensation mode for the fourth base station.

29. A method as defined in clause 27, wherein the fourth messageinstructs the second base station to act in compensation mode for afifth base station.

30. A method as claimed in any one of the preceding clauses, wherein theenergy saving mode data indicates that the first base station is of afirst network operator's network.

31. A computer program comprising instructions which, when the programis executed by a computer, cause the computer to carry out the method ofany one of the preceding clauses.

32. A base station comprising a transceiver, a processor and memory,wherein the processor is configured to perform the method of any one ofthe preceding clauses.

The invention claimed is:
 1. A method of operating a base station in acellular telecommunications network, the base station having a normalmode of operation, a compensation mode of operation and an energy savingmode of operation and being configured to switch between the normal modeof operation, the compensation mode of operation and the energy savingmode of operation, the method comprising: the first base station sendinga first message to a second base station, the first message includingenergy saving mode data for the first base station, the energy savingmode data relating to the first base station requesting that the secondbase station act in the compensation mode of operation for the firstbase station; the first base station receiving a second message, thesecond message being responsive to the energy saving mode data for thefirst base station, and including energy saving mode data for the secondbase station including a request that the first base station act in thecompensation mode of operation for the second base station; and thefirst base station entering the compensation mode of operation andcompensating for the second base station.
 2. A method of operating abase station in a cellular telecommunications network, the base stationhaving a normal mode of operation, a compensation mode of operation andan energy saving mode of operation and being configured to switchbetween the normal mode of operation, the compensation mode of operationand the energy saving mode of operation, the method comprising: thefirst base station receiving a first message from a second base station,the first message including energy saving mode data for the second basestation including a request that the first base station act in thecompensation mode of operation for the second base station; the firstbase station sending a second message to the second base station, thesecond message including energy saving mode data for the first basestation including a request that the second base station act in thecompensation mode of operation for the first base station; and the firstbase station entering energy saving mode.
 3. A non-transitory computerreadable storage element comprising instructions which, when executed bya computer, cause the computer to carry out the method of claim
 1. 4. Abase station comprising a transceiver, a processor and memory, whereinthe processor is configured to perform the method of claim
 1. 5. Anon-transitory computer readable storage element comprising instructionswhich, when executed by a computer, cause the computer to carry out themethod of claim
 2. 6. A base station comprising a transceiver, aprocessor and memory, wherein the processor is configured to perform themethod of claim 2.